Kotlin basic learning 14

Catalog

1.Kotlin Linguistic [] Operators learn

2.Kotlin Linguistic out - Covariant learning

3.Kotlin Linguistic in - Inverse learning

4.Kotlin Used in language in out

5.Kotlin Linguistic reified Keyword learning

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1.Kotlin Linguistic [] Operators learn

class KtBase108<INPUT>(vararg objects : INPUT, val isR:Boolean= true){
    // Turn on input Generic read-only mode 
    private val objectArray:Array<out INPUT> = objects
    //5 An explanation of the return type transformation 
    fun getR1() : Array<out INPUT> ? = objectArray.takeIf { isR }
    fun getR2() : Any = objectArray.takeIf { isR } ?: " You are a null"
    fun getR3() : Any ? = objectArray.takeIf { isR } ?: " You are a null" ?: null
    fun getR4(index : Int) : INPUT ? = objectArray[index].takeIf { isR } ?: null
    fun getR5(index : Int) : Any ? = objectArray[index].takeIf { isR } ?: "AAA" ?: 456 ?: 4856.63f ?:'C' ?: false ?: null
    operator fun get(index: Int) : INPUT ?= objectArray[index].takeIf { isR }
}
fun <INPUT> inputObj(item : INPUT){
    println((item as String?)?.length ?: " The generic data passed is null")
}
// TODO 108.Kotlin Linguistic [] Operators learn 
fun main(){
    inputObj("Bxb")
    inputObj("Wuwu")
    inputObj(null)
    println()
    val p1 : KtBase108<String?> = KtBase108(" Zhang San "," Li Si "," Wang Wu ",null)
    var r : String?=p1[0]
    val r2 :String? = p1[3]
    println(r)
    println(p1[1])
    println(p1[2])
    println(r2)
}

2.Kotlin Linguistic out - Covariant learning

// producer  out T  Covariance 
interface Producer<out T>{
    //out T  Represents the whole producer   This T  Can only be read , Cannot be modified 
    fun producer() : T
}
// consumer  in T  Inversion 
interface Consumer<in T>{
    //  Can only be modified 
    fun consumer(item : T)
}
// producer & consumer 
interface ProcuderAndConsumer<T>{
    fun consumer(item : T)
    fun procuder() : T
}
open class Animal
open class Humanity : Animal()
open class Man : Humanity()
open class Woman : Humanity()
class ProcuderClass1 : Producer<Animal>{
    override fun producer(): Animal {
        println(" producer  Animal")
        return Animal()
    }
}
class ProcuderClass2 : Producer<Humanity>{
    override fun producer(): Humanity {
        println(" producer  Humanity")
        return Humanity()
    }
}
class ProcuderClass3 : Producer<Man>{
    override fun producer(): Man {
        println(" producer  Man")
        return Man()
    }
}
class ProcuderClass4 : Producer<Woman>{
    override fun producer(): Woman {
        println(" producer  Woman")
        return Woman()
    }
}
// TODO 109.Kotlin Linguistic out - Covariant learning 
fun main(){
    val p1 : Producer<Animal> = ProcuderClass1() //ProcuderClass1  It's delivery  Animal, Certainly. 
    val p2 : Producer<Animal> = ProcuderClass2() //ProcuderClass2  It's delivery  Humanity, It's OK , because out
    val p3 : Producer<Animal> = ProcuderClass3() //ProcuderClass3  It's delivery  Man, It's OK , because out
    val p4 : Producer<Animal> = ProcuderClass4() //ProcuderClass4  It's delivery  Woman, It's OK , because out
    //out： Subclass objects of generics   I can assign a value to   Generic parent object 
    //out：  Generic concrete subclass objects   I can assign a value to   The parent object at the generic declaration 
}

3.Kotlin Linguistic in - Inverse learning

class ConsumerClass1 : Consumer<Animal>{
    override fun consumer(item : Animal) {
        println(" consumer  Animal")
    }
}
class ConsumerClass2 : Consumer<Humanity>{
    override fun consumer(item : Humanity) {
        println(" consumer  Humanity")
    }
}
class ConsumerClass3 : Consumer<Man>{
    override fun consumer(item : Man) {
        println(" consumer  Man")
    }
}
class ConsumerClass4 : Consumer<Woman>{
    override fun consumer(item : Woman) {
        println(" consumer  Woman")
    }
}
// TODO 110.Kotlin Linguistic in - Inverse learning 
fun main(){
    val p1 : Consumer<Man> = ConsumerClass1() //ConsumerClass1  It's delivery  Animal, Certainly. 
    val p2 : Consumer<Woman> = ConsumerClass2() //ConsumerClass2  It's delivery  Humanity, It's OK , because in
    // By default ： The parent class of the generic concrete   Cannot be assigned to   Of subclasses at the generic declaration 
    //in ：  The parent class of the generic concrete   It can be assigned to   Of subclasses at the generic declaration 
}

4.Kotlin Used in language in out

class SetClass<in T>(){
    // Function pair T It can only be modified , Cannot read 
    fun set1(item:T){
        println("set1  What you want to set item yes ：$item")
    }
    fun set2(item:T){
        println("set2  What you want to set item yes ：$item")
    }
    fun set3(item:T){
        println("set3  What you want to set item yes ：$item")
    }
}
class GetClass<out T>(_item : T){
    val item : T = _item
    // Function pair T Can only read , Do not modify 
    fun get1() :T{
        return item
    }
    fun get2() :T{
        return item
    }
    fun get3() :T{
        return item
    }
}
// TODO 115.Kotlin Used in language in out
fun main(){
    // Inversion  in  It can only be modified , Cannot read 
    val p1 = SetClass<String>()
    p1.set1("Bxb")
    p1.set2("Bob")
    println()
    // Covariance  out  Can only read , Do not modify 
    val p2 = GetClass(" Zhang San ")
    println(p2.get1())
    val p3 = GetClass(" Li Si ")
    println(p3.get2())
}

5.Kotlin Linguistic reified Keyword learning

data class ObjectClass1(val name : String,val age:Int,val study :String)
data class ObjectClass2(val name : String,val age:Int,val study :String)
data class ObjectClass3(val name : String,val age:Int,val study :String)
class KtBase112 {
    // By default, an object is output randomly , If this object is inconsistent with the object specified by the user , We will enable the standby object , Otherwise, the object is returned directly 
    inline fun<reified T> randomOrDefault(defaultLambdaAction:()->T):T?{
        val objList:List<Any> = listOf(ObjectClass1("obj1  Zhang San ",22," Study C++"),
                                        ObjectClass2("obj2  Li Si ",23," Study Java"),
                                        ObjectClass3("obj3  Wang Wu ",24," Study Python"))
        val randomObj : Any?= objList.shuffled().first()
        println(" The lucky ones you randomly generate are ：$randomObj")
        return randomObj.takeIf { it is T } as T?
            ?: defaultLambdaAction()
    }
}
// TODO 116.Kotlin Linguistic reified Keyword learning 
fun main(){
    val finalResult = KtBase112().randomOrDefault <ObjectClass1>{
        println(" Because the randomly generated object is inconsistent with the object we specify , So we use alternate objects ")
        ObjectClass1(" spare  obj1  Zhang San ",22," Study C++")
    }
    println(" Client end result ：$finalResult")
}